Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $94.78   12.474%   $106.6029   $106.60   $106.60   $106.60  
  Purchase #2 $189.61   7.273%   $203.4003   $203.40   $203.40   $203.40  
  Purchase #3 $172.34   13.727%   $195.9971   $196.00   $196.00   $196.00  
  Purchase #4 $66.81   6.718%   $71.2983   $71.30   $71.30   $71.30  
  Purchase #5 $26.69   9.719%   $29.284   $29.28   $29.30   $29.30  
  Purchase #6 $20.55   9.534%   $22.5092   $22.51   $22.50   $22.50  
  Purchase #7 $40.81   7.710%   $43.9565   $43.96   $43.95   $44.00  
  7 purchase totals = $611.59       $673.0483   $673.05   $673.05   $673.10